Lubricant compositions



United States Patent 3,505,222 LUBRICANT COMPOSITIONS Leonard M. Niebylski, Birmingham, Mich., assignor to Ethyl Corporation, New York, N.Y., a corporation of Virginia No Drawing. Filed Mar. 29, 1967, Ser. No. 626,701 Int. Cl. ClOm 5/14, 3/18, 7/36 US. Cl. 25217 2 Claims ABSTRACT OF THE DISCLOSURE The extreme pressure wear properties of base lubricants including water, hydrocarbons, polyesters, silicones, polyethers and halocarbons is enhanced by the addition of a synergistic mixture of a thiosulfate compound and a lead compound.

Background This invention relates to improved lubricant compositions. Many lubricants which are satisfactory for ordinary lubricating applications do not provide adequate protection under the extreme conditions of high load. These high load conditions are encountered in such applications as cutting oils, extrusion lubricants and bearing lubrication. Present lubricants made for these purposes include sulfurized and chlorinated hydrocarbon oils and oils containing such additives as iodine or molybdenum sulfide.

Summary An object of this invention is to provide an extreme pressure Wear additive for a variety of lubricating base oils. This additive greatly increases the lubricity of these base oils under conditions of extremely high load. This and other objects are accomplished by providing a synergistic friction-reducing composition comprising a mixture of at least two different compounds, said mixture comprising (A) from 1 to about 99 weight percent of a thiosulfate compound, and (B) from about 1 to 99 weight percent of a lead compound. The lubricity of a wide range of base lubricants is greatly improved by merely adding a friction-reducing amount of the above synergistic composition. The amount of synergistic mixture used can vary over a wide range depending upon the base lubricant employed and the specific application for which the lubricant is designed. Generally good results are obtained when from about 0.01 to 30 weight percent of the synergistic mixture is added. A more useful range of the synergistic mixture is from about 0.1 to 25 weight percent, and a most useful range is from about 0.5 to 20 weight percent of the synergistic mixture.

Useful thiosulfate compounds are those which contain the thiosulfate radical:

One class of such compounds consists of the metal salts of thiosulfuric acid such as the thiosulfates of lithium, sodium, potassium, calcium, barium, magnesium, strontium, zirconium, cadmium, zinc, nickel, manganese, cobalt, copper, aluminum, molybdenum, iron, lead, tin, silver, mercury, germanium, and the like. Of the foregoing, the more preferred thiosulfates are sodium thiosulfate and lead thiosulfate, with lead thiosulfate being the most preferred.

Another group of useful thiosulfate compounds are the metal salts of Bunte acids. Bunte acids are the reaction product of a mercaptan with sulfur trioxide. Their metal salts are represented by the formula:

i [RS--L|i0]uM (I) wherein R is a hydrocarbon radical containing from 1 to about 30 carbon atoms, M is a metal, and n is the valence of metal M. For example, when M is the monovalent sodium ion, 11 is 1.

The radical R can be an alkyl, cycloalkyl, aralkyl, alkaryl, or aryl radical. The radicals may contain other nonhydrocarbon substituents such as chloro, bromo, iodo, fiuoro, nitro, hydroxyl, nitrile, isocyanate, carboxyl, carbonyl, and the like.

The useful metals are all those capable of forming Bunte salts. Preferred metals are those previously listed as suitable for forming metal thiosulfates. Of these, the more preferred metals are sodium and lead, and lead is the most preferred metal in the Bunte salts.

Examples of useful Bunte salts include:

Thepreferred Bunte salts are those having Formula I wherein R represents an alkyl radical having from 1 to about 30 carbon atoms and M is sodium or lead. Examples of these are:

sodium S-lauryl thiosulfate lead S-lauryl thiosulfate sodium S-.( l-methylnonadecyl) thiosulfate lead S-methyl thiosulfate sodium S-triacontyl thiosulfate lead S-n-propyl thiosulfate The most preferred Bunte salt is lead S-lauryl thiosulfate.

Another useful class of thiosulfates are the quaternary ammonium thiosulfates. These are made by the reaction of quaternary ammonium halides with a metal thiosulfate as shown below.

Hence, another embodiment of this invention is a lubricating composition comprising a base lubricant and a friction-reducing amount of a mixture of at least two compounds, one of which is a lead compound 'and the other is a quaternary ammonium thiosulfate having Formula II wherein R R R and R are hydrocarbon radicals containing from 1 to about 30 carbon atoms. Some examples of the quaternary ammonium thiosulfates are: tetramethyl ammonium thiosulfate trimethyl lauryl ammonium thiosulfate triethyl lauryl ammonium thiosulfate trimethyl eicosyl ammonium thiosulfate trimethyl triacontyl ammonium thiosulfate trimethylphenyl ammonium thiosulfate trimethylbenzyl ammonium thiosulfate trimethyl (3,S-di-tert-butyl-4-hydroxybenzyl) thiosulfate trimethyl p-isoamylphenyl ammonium thiosulfate trimethyl p-isooctylbenzyl ammonium thiosulfate The other component forming the synergistic frictionreducing composition is a lead compound. It may be soluble or insoluble in the base lubricant. Some examples of suitable compounds include lead sulfide, lead carbonate, lead oxides, tetraalkylleads such as tetramethyllead, tetraethyllead, tetravinyllead, ethyltrimethyllead, dimethyldiethyllead, and the like.

Another class of lead components includes the previously-described Bunte salts wherein the metallic ingredient is lead. Oil solubility is imparted to the Bunte salt by the R radical. In order to accomplish this, it is preferred that the R group is an alkyl radical containing from about 10 to 30 carbon atoms. Of course, when the lead compound is a lead Bunte salt, the thiosulfate component must be a different thiosulfate including a Bunte salt of a metal other than lead compound in order to obtain the synergistic interaction.

The more preferred lead compounds are lead naphthenate, lead imidazole, lead isodecyl xanthogenate, lead oleate, lead stearate, lead sulfide, and lead n-octyl xanthogenate. Of the foregoing, the most preferred lead compound is lead naphthenate. The most preferred synergistic friction-reducing combination is a mixture of lead thiosulfate with lead naphthenate.

The following examples illustrate the synergistic friction-reducing compositions: 1 percent sodium thiosulfate plus 99 percent lead naphthenate; 99 percent sodium thiosulfate plus 1 percent lead naphthenate; 50 percent silver thiosulfate plus 50 percent lead sulfide; 75 percent aluminum thiosulfate plus 25 percent lead S-lauryl thiosulfate; and 25 percent trimethyl lauryl ammonium thiosulfate plus 75 percent lead imidazole.

Suitable base lubricants include hydrocarbon-derived lubricating oils and greases, polyester lubricants, silicone oils, polyethylene oils, and halohydrocarbons.

Hydrocarbon oils include those of a wide viscosity range of from about SAE-S to SAE-90. These oils can be prepared using any of the well-known refining methods such as solvent refining. When the oils are to be used as cutting oils, it is preferred that they have a viscosity of about 100 SUS at 100 F. Typical hydrocarbon oil formulations of this invention are represented by the following examples, in which all percentages are by Weight.

EXAMPLE 1 To a Pennsylvania neutral mineral oil having a viscosity of 185 SUS at 100 F. is added 1.0 percent of lead thiosulfate and 3 percent of lead as lead naphthenate.

EXAMPLE 2 To a mid-continent, solvent-refined neutral mineral oil having a viscosity of 290 SUS at 100 F. is added 3 percent of sodium thiosulfate and 1 percent lead as lead S-lauryl thiosulfate.

EXAMPLE 3 To a California neutral mineral oil having a viscosity of 382 SUS at 100 F. is added 5 percent of potassium thiosulfate and 0.1 Weight percent of lead as tetraethyllead.

EXAMPLE 4 In a solvent-refined paraffinic mineral oil having a viscosity of 155 SUS at 100 F. is slurried 20% of a zinc S-isoamyl thiosulfate and 1 percent lead as lead xanthate.

4 EXAMPLE 5 To a solvent-extracted Pennsylvania bright stock having a viscosity of 500 SUS at F. is added 7 percent of lead S-octadecyl thiosulfate and 3 percent of lead as lead imidazole.

EXAMPLE 6 To a polybutene oil having a viscosity of 114 SUS at 100 F. is added 0.5 percent of a finely-divided lead thiosulfate and 1 percent of lead as lead naphthenate.

EXAMPLE 7 To a polymerized trimethylethylene having a viscosity of 367 SUS at 100 F. is added 3 percent of a finelydivided silver thiosulfate and 0.1 percent of lead as lead S-triacontyl thiosulfate.

The synergistic additives are useful in a wide range of hydrocarbon-derived greases containing various metal soaps as thickening agents such as calcium stearate, lead oleate or sodium oleate. The following examples will serve to illustrate the use of the synergistic mixtures as extreme pressure friction-reducing agents in some hydrocarbon-derived greases.

EXAMPLE 8 To a calcium oleate thickened grease containing about 82 percent of a hydrocarbon oil having a Saybolt viscosity at 100 F. of 300 is added 5 percent of lead thiosulfate and 3 percent of lead as lead naphthenate.

EXAMPLE 9 To a lead oleate thickened grease containing about 94 percent of a Pennsylvania mineral oil having 21 Saybolt viscosity at 100 F. of 200 is added 3 percent of sodium thiosulfate and 1 percent of lead as lead imidazole.

EXAMPLE 10 To a calcium stearate thickened grease containing about 87 percent of a California mineral oil having a Saybolt viscosity at 100 F. of 241 is added 20 percent of barium S-isoamyl thiosulfate and 5 percent of lead as lead naphthenate EXAMPLE 11 To a grease containing 88 percent of a California mineral oil having a Saybolt viscosity at 100 F. of 300 and thickened with a mixture of calcium stearate and calcium oleate is added 15 percent of tetramethyl ammonium thiosulfate and 5 percent of lead as triethyllead chloride.

The polyester lubricant base materials used in formulating' the lubricant compositions of my invention may be either oils or greases. The oils may be formed by the reaction of a polycarboxylic acid with a mono-hydric alcohol, the reaction of a polyhydric alcohol with a mono-carboxylic acid, reaction between a polyhydric alcohol and a polycarboxylic acid, or combinations of the above reactions, such as, for example, reaction of a dicarboxylic acid with a glycol and a mono-hydric alcohol, reaction of a glycol with a dicarboxylic acid and a mono-carboxylic acid, or the reaction of a glycol, a mono-hydric alcohol, a dicarboxylic acid and a monocarboxylic acid. The acids may be mono-carboxylic aliphatic acids such as, for example, propionic acid, valeric acid, Z-ethyl enanthic acid, 2,2-di-propyl butyric acid or 3-(2-methylhexyl) valeric acid. They may contain unsaturated linkages, such as, for example, in senecioic acid, sorbic acid, or angelic acid; they may be polycarboxylic aliphatic acids such as succinic acid, glutaric acid, azelaic acid, 5-octene-l,8-dicarboxylic acid, or 3-hexene-2,3,4-tricarboxylic acid, and they may be aromatic or cycloaliphatic acids, such as cyclohexaneacetic acid, 1,4-cyclopentylenebis acetic acid, phthalic acid, hemimellitic acid, and terephthalic acid.

The alcohols used in preparing the polyester lubricant base materials may be aliphatic mono-hydrie alcohols such as propanol, 2-ethyl-3-hexanol, 2-ethyl-4-propyl heptanol, 2-butanol, or Z-methyl propanol. They may be polyhydric aliphatic alcohols, such as, 1,6-hexamethylene glycol, 1,10-decamethylene glycol, 2-hexene-1,'6-diol, and 1,6- heptylene glycol, and they may be monoor polyhydric alicyclic or aromatic alcohols, such as 4-[m-(2-hydroxyethyl)phenyl]butanol, 3 (2 hydroxyethyl)cyclohexanebutanol, p-(hydroxymethyl)phenethyl alcohol, a-rnethylp-xylene 01,01 diol, 1,4-cyclohexane-;3,5-diethyl-di-methanol, 2,3-bis(4-hydroxybutyl)-benzy1 alcohol, 4,4-[3-(3- hydroxyhexyl)-o-phenylene]dibutanol, and 5-[3-(3 hydroxypropyl)cyclopenta 2,4-dienyleneJ-3-ethyl a myl alcohol.

The polyester base greases used in formulating lubricant compositions of the invention are formed by admixing a soap with a diester oil. Such soaps may be derived from animal or vegetable fats or fatty acids, wool grease; rosin, or petroleum acids. Typical examples of such soaps are lead oleate, lithium stearate, aluminum tristearate, calcium glycerides, sodium oleate, and the like. In addition, the diester greases may contain unreacted fat, fatty acids, and alkali; unsaponifiable matter including glycerol and fatty alcohols; rosin or wool grease; water; and certain additives which may function as modifiers or peptizers.

The preferred diester lubricant materials used in formulating the preferred lubricant compositions have the following generic formula:

Where R is a divalent aliphatic hydrocarbon radical which may be saturated or unsaturated and has from 2 to carbon atoms and R and R are branched chain alkyl groups having from about 4 to 20 carbon atoms.

As shown by the above generic formula, the diesters utilized in formulating the preferred lubricant compositions include esters of succinic, glutaric, adipic, pimelic, suberic, azelaic and sebacic acid. Typical examples of such esters are di-isooctyl azelate, di(2-ethylhexyl)sebacate, di-secamyl sebacate, diisooctyl adipate, di(2-ethylhexyl)adipate, di(2-ethylhexyl)azelate, di(1-methyl 4 ethyloctyl)glutarate, di-isoamyl adipate, di(2-ethylhexyl) glutarate, di(2- ethylbutyl)adipate, di-tetradecyl sebacate and di(2-ethylhexyl)pinate.

The more preferred diesters are prepared by esterifying one mole of a dicarboxylic acid having the general formula: HOOC(CH COOH, where x is an integer of from 2 to 8, with 2 moles of a branched chain alcohol containing from about 4 to about 16 carbon atoms. Typical of the reactions embraced herein are the reactions of succinic, glutaric, adipic, pimelic, suberic, or azelaic acid with sec-amyl alcohol, 3-methyl butanol, 2-ethyl hexanol or the branched chain secondary alcohols undecanol or tetradecanol.

The preferred diester lubricant fluids have molecular weights ranging from about 300 to about 600 and freezing and pouring points from about 40 to less than about 100 F. The flash and fire points range from about 300 F. to about 500 F. and their spontaneous ignition temperatures range from about 100 to about 800 F. The diesters made by reacting a dicarboxylic acid with a branched chain alcohol have been found to have superior viscometric properties as compared with diesters made by reacting dihydric alcohols with mono-carboxylic acids, and thus, diesters prepared by the former method are preferred in formulating the lubricant compositions of my invention.

In formulating the polyester grease compositions within the scope of my invention, I have found that the greases prepared by admixing a lithium soap with the polyester oils have superior oxidative stability as compared with greases formulated with other soaps, such as, for example, the sodium, calcium or lead soaps. Thus, the polyester greases employing a lithium soap constitute a preferred embodiment of lubricant compositions within the scope of my invention.

To further illustrate the lubricant compositions of my invention, the following examples show typical ester lubricant compositions within the scope of the present invention. Unless otherwise specified, the percent composition given in these examples is on a weight basis.

EXAMPLE 12 To diisooctyl adipate having a viscosity of 35.4 SUS at 210 F. is added 10 percent of calcium thiosulfate and 0.5 percent of lead as lead imidazole.

EXAMPLE 13 To di( l-methyl-4-ethyloctyl)glutarate is added 0.1 percent of lead thiosulfate and 5 percent of lead as lead naphthenate.

EXAMPLE 14 To di(2-ethylhexyl)adipate is added 25 percent of an equal mole mixture of cuprous thiosulfate and sodium thiosulfate and 7 percent of lead as lead naphthenate.

EXAMPLE 15 To diethylphthalate is added 3 percent of lead thiosulfate, 2 percent of tin thiosulfate and 0.5 percent of lead as lead S-lauryl thiosulfate.

EXAMPLE 16 To di-sec-amyl sebacate having a viscosity of 34.2 SUS at 210 F. is added 10 percent of lead S-(3,5-di-tert-butyl- 4-hydroxybenzyl)thiosulfate and 7 percent of lead as lead naphthenate.

EXAMPLE 17 To di(2-ethylhexyl)sebacate having a viscosity of 37.4 SUS at 210 F. is added 7 percent of trimethyl lauryl ammonium thiosulfate and 7 percent of lead as lead S-(lmethylheptadec-yl) thiosulfate.

The term silicone as used in this specification refers to a group of synthetic compounds containing silicon and organic groups. Silicone oils are Well known to have a high degree of thermal stability and can be used at very high temperatures. Their viscosity index is high and the silicone oils and greases change relatively little in flow properties over a wide temperature range. In spite of these desirable characteristics, however, the widespread adoption of silicone oils has been hampered because they have relatively poor lubricity as compared with conventional hydrocarbon oils. The present invention alleviates this problem, especially under extreme pressure conditions. It is, therefore, an object of this invention to provide silicone lubricants, both greases and oils, with improved lubricity. The silicone oils and greases serving as the base lubricant in this embodiment of the invention include the polysiloxane oils and greases of the type polyalkyl-, polyaryl-, polyalkoxy-, and polyaryloxy, such as polydimethylsiloxane, polymethylphenylsiloxane, and polymethoXyphenoxysiloxane. Also included are silicate ester oils such as tetraalkyloxy and tetraaryloxy silanes of the tetra-Z-ethylhexyl and tetra-p-tert-butylphenyl types and the silanes. Also included are the halogen-substituted siloxanes such as the chlorophenylpolysiloxanes. The polyalkyl-, polyaryland polyalkylpolyarylsiloxanes are the preferred types of silicone base lubricants. The following examples illustrate typical silicon base lubricants containing the synergistic additives. The percentages given are on a weight basis.

EXAMPLE 18 To Dow-Corning 200 silicon fluid (a dimethylpolysiloxane) having a viscosity of centistokes at 25 C., an open cup flash point of 575 F., a pour point of 67 F., and a specific gravity of 0.97 at 77 F. is added 5 percent of a finely-ground lead thiosulfate and 3 percent of lead as lead naphthenate.

7 EXAMPLE 19 To some Dow-Corning 710 silicon fluid (a phenylmethylpolysiloxane of high phenyl content) having a viscosity of 475-525 centistokes at 25 C. and an open cup flash point of 575 F. is added 0.1 percent of sodium thiosulfate powder and 2 percent of lead as lead S-lauryl thiosulfate.

EXAMPLE 20 To Dow-Corning 44 silicon grease (a polymethylpolyphenylsiloxane grease of medium consistency having a serviceable temperature range of from 30 to 400 F.) is added 25 percent of nickel thiosulfate and 1 percent of lead as lead imidazole.

EXAMPLE 21 To Dow-Coming 550 silicon oil (a phenylmethylpolysiloxane having a viscosity of 100-150 centistokes at 25 C.) is added 5 percent of a finely-divided iron thiosulfate powder and 0.1 percent of lead as lead naphthenate.

EXAMPLE 22 To monoethyldiethoxy monoacetoxysilane liquid having a boiling point of 191.5 C. is added 10 percent of lead thiosulfate and 4 percent of lead as tetraethyllead.

EXAMPLE 23 To tribenzyl-n-hexadecylsilane liquid having a boiling point of 245-248 C. is added 20 percent of barium thiosulfate and 0.5 percent of lead as lead S-lauryl thiosulfate.

EXAMPLE 24 To a plyphenylpolymethylsiloxane (Dow-Corning F-60 fluid having a viscosity of 71 centistokes at 25 C.) is added 15 percent of a finely-divided lead thiosulfate powder and 2 percent of lead as lead naphthenate.

The synthetic polyether base lubricants are generally polyalkylene oxide derivatives of aliphatic alcohols or phenols. They are frequently referred to as polyalkylene glycol oils and greases. The alkylene oxides most frequently used in their preparation are ethylene and propylene oxide. Also included within this group are the reaction products formed from higher polyalkylene oxides, polyglycidyl ethers and polythioglycols. Many of these substances are manufactured and marketed under the tradename Ucon." They are useful lubricants because of their high viscosity index and low viscosity in sub-zero temperature ranges. They generally have viscosities of from about 135-1200 SUS at 100 F. Tetrahydrofuran copolymer oils and greases are formed by the copolymerization of tetrahydrofuran and an alkylene oxide such as ethylene oxide. These are also included Within the polyether lubricant bases. The following examples will serve to illustrate this embodiment of the invention.

EXAMPLE 25 To a polyalkylene oxide oil derived from the reaction of lauryl alcohol with ethylene oxide and having a molecular Weight of about 2000 is added percent of lead thiosulfate and 5 percent of lead as lead naphthenate.

EXAMPLE 26 To a polyether lubricant base formed by the reaction of p-isooctylphenol with propylene oxide and having an average molecular weight of about 2500 is added 0.1 percent sodium S-ethyl thiosulfate and 1 percent of lead as lead imidazole.

EXAMPLE 27 To a tetrahydrofuran ethylene oxide copolymer oil having a viscosity of 83 SUS at 210 F. is added 25 percent of tetramethyl ammonium thiosulfate and 5 percent of lead as lead S-(3,5-di-tert-butyl-4-hydroxybenzyl) thiosulfate.

Another useful base lubricant is water. Although not as eflective as many other base lubricants, it finds use in applications such as cutting lubricants because of its low cost. Especially useful thiosulfates in water are the watersoluble metal thiosulfates such as those derived from alkali metals, calcium, strontium, magnesium, cadmium, zinc, nickel, cobalt, iron, and manganese. Another useful class is a mixture of an alkali metal thiosulfate with a normally insoluble metal thiosulfate such as lead, mercury or copper thiosulfate. This serves to solubilize the normally insoluble thiosulfate. In the case of the combination of an alkali metal thiosulfate with lead thiosulfate, it is also a convenient method of adding a thiosulfate additive and a lead additive which is soluble in the aqueous base lubricant. Other useful soluble lead compounds include lead nitrate and lead acetate. From the foregoing, it is not meant to imply that the thiosulfate additives or the lead additive must be soluble in the base lubricant because the combination is very useful when one or both components of the synergistic combination are merely dispersed in the base lubricant.

Tests have been conducted to demonstrate the extreme pressure Wear reducing properties of the mixtures of thiosulfate compounds and lead compounds in base lubricants. These tests were conducted using an Extreme Pressure Lubricant Tester (EP Tester), described by Boerlage in Engineering, vol. 136, July 14, 1933, pp. 46-7. This test machine employs 4 balls an'anged in a tetrahedron. The bottom 3 balls are firmly held in a non-rotatable fixture such that the balls are in abutting relation to each other. Their centers form the apices of an equilateral triangle. The top ball is afiixed to a rotatable spindle whose axis is positioned perpendicularly to the plane of the nonrotatable ball in a line with the center point of the triangle formed by the apices of the 3 bottom balls.

In operation, the 4 balls are immersed in the lubricant composition to be tested and the fixture holding the 3 bottom balls is moved upwardly forcing the 3 fixed balls against the upper rotating ball. The severity of the test can be changed by merely forcing the lower fixture upward under different pressures. When the pressure reaches the point that the lubricant fails, the heat generated by the friction between the rotating ball and the fixed balls is such that the balls weld together. In this test, the presently-known extreme pressure lubricants such as those containing sulfurized sperm oil will weld at loads in the range of from 200 to 450 kg. The following table shows the results obtained when various additives were added in different concentrations to a base hydrocarbon lubricant, Amoco No. 31, used as a cutting oil.

TABLE 1 v Cone. Weld Loa Additive (Percent) (kg.)

10 {Lead naphthenate. Lead thiosulfate. u Lead naphthena Lead thiosnlfatem 12 Lead naphthenate Lead thiosulfatem 13 Sodium thiosulfate 5 Sodium thiosulfate Triethyllead xanthate- 16 Sodium thiosulfate. Lead imidazole 17 Sodium thiosulfate Lead imidazole 1 Concentration of lead-containing materials is in terms of weight percent lead and the concentration of nonlead additives is based on the weight percent of the additive.

1 800 means that the equipment could not cause weld at its limit, which is 800 kg. This represents a metal contact pressure of about 1,000,000 pounds per square inch.

The same EP test was carried out employing high viscosity draw base hydrocarbon lubricants such as used in metal extruding operations. The following results were obtained.

The above results clearly show the synergistic effect of the combination of a thiosulfate compound and a lead compound. In Table l, the cutting oil alone welded at a 100 kg. load. The addition of percent lead, as lead naphthenate, raised the weld load to 200 kg. (Item 2). The use of 1 percent lead, as lead thiosulfate, alone raised the weld load to 450 kg. (Item 3). However, the combination of the two (Item resulted in a lubricant that prevented weld at 800 kg., the load limit of the EP tester.

A similar effect was obtained when sodium thiosulfate was used as the thiosulfate compound. As Items 4 and 5 show, sodium thiosulfate has a load rating of 450500 kg, and the load rating changes very little with concentration. Lead sulfide (Item 8) has a load rating of 360 kg. The combination of sodium thiosulfate with lead sulfide (Item 13) results in a load rating of 700 kg.

An unusual feature of the invention is that the lead atom and the thiosulfate radical must be in two different compounds to obtain the synergistic effect. For example, lead thiosulfate, a useful EP additive by itself, has both a lead atom and a thiosulfate radical. It has an EP load rating at 1 weight percent of 450 kg. (Item 3). However, the combination of lead naphthenate, which has a load rating of 200 kg. at 5 percent (Item 2), with sodium thiosulfate, which alone has a 500 kg. rating at 5 percent (Item 5), gives even more eifect than is obtained from the same amount of lead, as lead thiosulfate. As shown in Item 14, 1 percent lead, as lead naphthenate, in combination with 5 percent of sodium thiosulfate results in an EP load rating of 700 kg.

The beneficial effect of the combination is obtained even when the thiosulfate compound also contains lead. For example, lead thiosulfate is improved to an unexpected degree when it is used in combination with a different lead compound. For example, lead thiosulfate at the 2 /2 percent level imparts a 200 kg. load rating to a draw lubricant (Table 2, Item 20). Lead naphthenate imparts about the same rating to the draw lubricant (Item 19). When the two additives are used in combination the EP rating of the draw lubricant exceeds 800 kg., the test limit of the EP tester.

I claim:

1. A synergistic friction-reducing composition comprising a mixture of:

(A) from 1 to about 99 weight percent of lead thiosulfate, and

(B) from 1 to about 99 Weight percent of lead naphthenate.

2. A lubricant composition comprising a major amount of a hydrocarbon base lubricant selected from lubricating oils and greases and an extreme pressure friction-reducing quantity of a composition of claim 1.

References Cited UNITED STATES PATENTS 2,288,288 6/1942 Lincoln 25246.4 X 2,330,239 9/1943 Prutton 252-33 X 2,331,005 10/1943 Storey et a1. 25233 X 2,338,613 1/1944 Zimmer 25237.7 3,377,279 4/1968 Sibert 25225 X DANIEL E. WYMAN, Primary Examiner W. CANNON, Assistant Examiner US. Cl. X.R. 

